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+<!-- doc/src/sgml/tcn.sgml -->
+
+<sect1 id="tcn" xreflabel="tcn">
+ <title>tcn</title>
+
+ <indexterm zone="tcn">
+  <primary>tcn</primary>
+ </indexterm>
+
+ <indexterm zone="tcn">
+  <primary>triggered_change_notification</primary>
+ </indexterm>
+
+ <para>
+  The <filename>tcn</filename> module provides a trigger function that notifies
+  listeners of changes to any table on which it is attached.  It must be
+  used as an <literal>AFTER</literal> trigger <literal>FOR EACH ROW</literal>.
+ </para>
+
+ <para>
+  This module is considered <quote>trusted</quote>, that is, it can be
+  installed by non-superusers who have <literal>CREATE</literal> privilege
+  on the current database.
+ </para>
+
+ <para>
+  Only one parameter may be supplied to the function in a
+  <literal>CREATE TRIGGER</literal> statement, and that is optional.  If supplied
+  it will be used for the channel name for the notifications.  If omitted
+  <literal>tcn</literal> will be used for the channel name.
+ </para>
+
+ <para>
+  The payload of the notifications consists of the table name, a letter to
+  indicate which type of operation was performed, and column name/value pairs
+  for primary key columns.  Each part is separated from the next by a comma.
+  For ease of parsing using regular expressions, table and column names are
+  always wrapped in double quotes, and data values are always wrapped in
+  single quotes.  Embedded quotes are doubled.
+ </para>
+
+ <para>
+  A brief example of using the extension follows.
+
+<programlisting>
+test=# create table tcndata
+test-#   (
+test(#     a int not null,
+test(#     b date not null,
+test(#     c text,
+test(#     primary key (a, b)
+test(#   );
+CREATE TABLE
+test=# create trigger tcndata_tcn_trigger
+test-#   after insert or update or delete on tcndata
+test-#   for each row execute function triggered_change_notification();
+CREATE TRIGGER
+test=# listen tcn;
+LISTEN
+test=# insert into tcndata values (1, date '2012-12-22', 'one'),
+test-#                            (1, date '2012-12-23', 'another'),
+test-#                            (2, date '2012-12-23', 'two');
+INSERT 0 3
+Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
+Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
+Asynchronous notification "tcn" with payload ""tcndata",I,"a"='2',"b"='2012-12-23'" received from server process with PID 22770.
+test=# update tcndata set c = 'uno' where a = 1;
+UPDATE 2
+Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
+Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
+test=# delete from tcndata where a = 1 and b = date '2012-12-22';
+DELETE 1
+Asynchronous notification "tcn" with payload ""tcndata",D,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
+</programlisting>
+ </para>
+
+</sect1>